Final answer:
Fuel transfer valves can be closed using a stopcock or valve, a solenoid valve, or by an automatic control system.
Step-by-step explanation:
Once opened to transfer fuel, the fuel transfer valves can be closed by different mechanisms depending on the specific system. One common method is to use a stopcock or valve that can be manually turned to block the flow of fuel.
Another approach is to use a solenoid valve, which is an electrically controlled valve that can be opened or closed by applying or removing an electrical current.
In some cases, the fuel transfer valves may also be automatically closed by a control system when certain conditions are met, such as reaching a specific pressure or temperature limit.